"The Russian side [has] indicated its readiness to participate in joint efforts by the interested parties aimed at a peacefuldiplomatic resolution of the situation surrounding North Korea," a statement issued by the Russian foreign ministry said.

US anger

George Bush, the US president, has called the communist state's claim of a nuclear test a provocative act and has warned Pyongyang against exporting nuclear material.

Bush said late on Monday: "Once again, North Korea has defied the will of the international community, and the international community will respond.

"Once again North Korea has defied the will of the international community, and the international community will respond"

George Bush, US president

"The transfer of nuclear weapons or material by North Korea to states or nonstate entities would be considered a grave threat to the United States.

"And we would hold North Korea

fully accountable for the consequences of such action."

John Bolton, the US ambassador to the UN, described the standoff with Pyongyang as one "between North Korea and the rest of the world".

"I think that North Korea has had a successful history of intimidating other countries," Bolton said on CBS television.

"They're not going to be successful with us."

The US and Japan have discussed imposing sanctions against North Korea.

Uncertainty over test

Despite the strong diplomatic language on all sides, there is growing uncertainty over whether or not North Korea actually conducted a nuclear test.

The US Geological Survey initially said it had detected a 4.2 magnitude quake in North Korea on Monday, confirming a similar report from South Korea.

However scientists have since scaled back their initial estimates that the quake indicates an explosion similar in size to that which destroyed Hiroshima in 1945. Estimates now indicate that the explosion may have been much smaller.

Shinzo Abe, the new Japanese prime minister, said that the small size of the explosion and secrecy of the North Korean government could make the test difficult for the Japanese government to confirm.

"We would like to gather information and confirm it, but there are views that it may be difficult to verify it," Abe said.

No radiation detected

Japan also said on Tuesday that no unusual radiation had been detected in dust samples collected by its military planes.

South Koreans protested angrily against the reported nuclear test

"So far, no abnormal amount of radioactive particles has been detected," said a report submitted to a Japanese special government task force dealing with possible fallout from the alleged underground test.

Scientists speculate the explosion could have been caused by conventional weapons exploded as a bluff by North Korea, or that the nuclear weapon had misfired.

In a symbolic move, Japanese parliamentarians have also passed a non-binding resolution condemning the North Korean announcement.

"We, as the only nation to experience an atomic bombing, something humanity should never suffer again, are devoting ourselves to swift efforts to abolish nuclear weapons," Ichiro Aisawa, a senior ruling party politician, said as he proposed the resolution to parliament's lower house.